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Message-ID: <20070511110754.GA13985@elte.hu>
Date: Fri, 11 May 2007 13:07:54 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Kasper Sandberg <lkml@...anurb.dk>
Cc: Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Con Kolivas <kernel@...ivas.org>,
Nick Piggin <npiggin@...e.de>,
Arjan van de Ven <arjan@...radead.org>,
Peter Williams <pwil3058@...pond.net.au>,
Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
Willy Tarreau <w@....eu>,
Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>
Subject: Re: [patch] CFS scheduler, -v11
[ remailing this on-list too, with some more explanations, i suspect
others might be affected by this 3D performance problem as well. ]
* Kasper Sandberg <lkml@...anurb.dk> wrote:
> [...] but under harder load such as pressing a link in a browser while
> 3d(at nice 0), or spamasassin at nice 0 still makes it go stutterish
> instead of smooth. But overall it does seem better.
ok, i think i have finally managed to track this one down.
certain 3D drivers grew a subtle performance dependency on a
sys_sched_yield() implementation/behavioral bug/misbehavior of the
upstream kernel, which implementation SD does too, but CFS fixes it by
always yielding efficiently. The result of this bug/dependency is
extremely low FPS during any CPU-intense workload.
you are using an Nvidia 6600 card so i dont know for sure whether you
are affected by this problem (Radeon cards are affected and i can now
reproduce that) - but the symptoms i've reproduced seem to be matching
your system's symptoms.
I've added a workaround for this to CFS, do you have some time to try
it? I've attached the sched-cfs-v12-rc4.patch (delta patch ontop of a
CFS -v11 tree), and once you have booted it you can activate the
workaround via:
echo 1 > /proc/sys/kernel/sched_yield_bug_workaround
does this make any difference to the drastic 3D smoothness problems you
are experiencing?
Ingo
---
Makefile | 2 +-
drivers/char/drm/radeon_cp.c | 5 +++++
include/linux/sched.h | 2 +-
kernel/sched_fair.c | 23 +++++++++++++++++++----
kernel/sysctl.c | 12 ++++++------
5 files changed, 32 insertions(+), 12 deletions(-)
Index: linux/Makefile
===================================================================
--- linux.orig/Makefile
+++ linux/Makefile
@@ -1,7 +1,7 @@
VERSION = 2
PATCHLEVEL = 6
SUBLEVEL = 21
-EXTRAVERSION = -cfs-v11
+EXTRAVERSION = -cfs-v12
NAME = Nocturnal Monster Puppy
# *DOCUMENTATION*
Index: linux/drivers/char/drm/radeon_cp.c
===================================================================
--- linux.orig/drivers/char/drm/radeon_cp.c
+++ linux/drivers/char/drm/radeon_cp.c
@@ -2210,6 +2210,11 @@ int radeon_driver_load(struct drm_device
DRM_DEBUG("%s card detected\n",
((dev_priv->flags & RADEON_IS_AGP) ? "AGP" : (((dev_priv->flags & RADEON_IS_PCIE) ? "PCIE" : "PCI"))));
+ if (sysctl_sched_yield_bug_workaround == -1) {
+ sysctl_sched_yield_bug_workaround = 1;
+ printk(KERN_WARNING "quirk installed: turning on "
+ "sys_sched_yield() workaround for Radeon DRM.\n");
+ }
return ret;
}
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -1253,9 +1253,9 @@ extern char * sched_print_task_state(str
extern unsigned int sysctl_sched_granularity;
extern unsigned int sysctl_sched_wakeup_granularity;
-extern unsigned int sysctl_sched_sleep_history_max;
extern unsigned int sysctl_sched_child_runs_first;
extern unsigned int sysctl_sched_load_smoothing;
+extern int sysctl_sched_yield_bug_workaround;
#ifdef CONFIG_RT_MUTEXES
extern int rt_mutex_getprio(struct task_struct *p);
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -18,10 +18,6 @@
*/
unsigned int sysctl_sched_granularity __read_mostly = 2000000;
-unsigned int sysctl_sched_sleep_history_max __read_mostly = 2000000000;
-
-unsigned int sysctl_sched_load_smoothing = 0 | 0 | 0 | 8;
-
/*
* Wake-up granularity.
* (default: 1 msec, units: nanoseconds)
@@ -32,6 +28,19 @@ unsigned int sysctl_sched_load_smoothing
*/
unsigned int sysctl_sched_wakeup_granularity __read_mostly = 0;
+unsigned int sysctl_sched_load_smoothing __read_mostly = 0 | 0 | 0 | 8;
+
+/*
+ * sys_sched_yield unfairness bug workaround switch.
+ * (default: -1:auto-detect+disabled. Other values: 0:disabled, 1:enabled)
+ *
+ * This option switches the unfair yield implementation of the
+ * old scheduler back on. Needed for good performance of certain
+ * apps like 3D games on Radeon cards.
+ */
+int sysctl_sched_yield_bug_workaround __read_mostly = -1;
+
+EXPORT_SYMBOL_GPL(sysctl_sched_yield_bug_workaround);
extern struct sched_class fair_sched_class;
@@ -462,6 +471,12 @@ yield_task_fair(struct rq *rq, struct ta
u64 now;
/*
+ * Bug workaround for 3D apps running on the radeon 3D driver:
+ */
+ if (unlikely(sysctl_sched_yield_bug_workaround > 0))
+ return;
+
+ /*
* yield-to support: if we are on the same runqueue then
* give half of our wait_runtime (if it's positive) to the other task:
*/
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -223,24 +223,24 @@ static ctl_table kern_table[] = {
},
{
.ctl_name = CTL_UNNUMBERED,
- .procname = "sched_sleep_history_max_ns",
- .data = &sysctl_sched_sleep_history_max,
+ .procname = "sched_child_runs_first",
+ .data = &sysctl_sched_child_runs_first,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = &proc_dointvec,
},
{
.ctl_name = CTL_UNNUMBERED,
- .procname = "sched_child_runs_first",
- .data = &sysctl_sched_child_runs_first,
+ .procname = "sched_load_smoothing",
+ .data = &sysctl_sched_load_smoothing,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = &proc_dointvec,
},
{
.ctl_name = CTL_UNNUMBERED,
- .procname = "sched_load_smoothing",
- .data = &sysctl_sched_load_smoothing,
+ .procname = "sched_yield_bug_workaround",
+ .data = &sysctl_sched_yield_bug_workaround,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = &proc_dointvec,
-
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